The nameplates on CEO offices are changing at what appears to be an historic pace. In the first 11 months of the year, 1,991 CEOs announced their departures, according to a report from outplacement firm Challenger, Gray & Christmas. That’s up 16% compared with the same timeframe last year and the highest tally on record since the firm began tracking CEO changes in 2002. This year’s high-profile breakups included Nike and John Donahoe, Intel and Pat Gelsinger, and Boeing and Dave Calhoun. With the economy going strong, the stock market on a two-year bull run, and consumer spending trending upward,...